Every year, the U.S. National Weather Service (NWS) launches over 70,000 weather balloons to study the atmosphere. These balloons provide the most cost effective way of recording important atmospheric data up to the very edge of Earth's atmosphere. Each balloon carries an instrumentation package called a radiosonde.
Radiosondes weigh between 250 and 500 grams and transmit data such as GPS location (for winds aloft), temperature, humidity, and pressure back to a ground station for the duration of the flight. Radiosondes used by the National Weather Service are the most common models; they ascend by balloon at a rate of 1000 feet per minute and transmit the data they collect using 300 milliwatt or less transmitters on the 400 MHz meteorological band. Once the balloon bursts, the radiosonde falls back to earth with a small parachute designed to prevent it from hitting the ground hard enough to harm people or property.
Unfortunately, of the 70,000+ weather balloon launches per year, less than 20% of the radiosondes are recovered. While radiosondes are usually physically capable of reuse, the issue lies in the lack of a cohesive recovery effort. The only means for radiosonde recovery is to be found by a passer-by who sends it back to the NWS using the mailer included with every unit. At a cost of roughly $290 per unit, the annual cost of lost radiosondes is substantial.